This invention relates generally to differential mechanisms and more particularly to a limited slip differential mechanism having a biasing mechanism to apply a preload upon clutch members of the mechanism.
As is well known, automotive differential gearing is necessary to transmit motion from the engine to an axle of the vehicle through differential gearing to give an equal tractive force to each of two wheels and, at the same time, permit either of them to run ahead or lag behind the other as may be required in rounding curves or riding over obstructions. The axle is not formed of one solid piece, but motion is transmitted to the right and left hand wheels by means of separate sections, the inner ends of which are attached to the side gears of the differential mechanism. During turning and differential action by the mechanism, one side gear associated with the outer wheel turns faster than the side gear coupled to the inner wheel while both wheels continue to receive driving force.
Such mechanisms adequately solve the problem on dry pavement or other comparatively hard surfaces. However, for example, in snow or mud, in the event that one of the two driven wheels begins to slide or freely rotate, there is essentially no torque transmitted to the other of the pair of driven wheels and the vehicle is stuck simply because one of its two driven wheels is allowed to slip.
To overcome this problem, slip limiting differentials have been developed which provides a clutch within the differential mechanism so that differentiation may occur only after a predetermined torque level is reached. This ensures that both of the driven wheels will receive at least this predetermined minimum torque, even though one of the two wheels is sliding. One such limited slip differential mechanism employs a stacked series of clutch plates and discs each of generally flat, annular configuration with the plates and discs spring biased into contact with one another to provide a friction coupling between the differential case and one side gear with clutch slippage occurring only after a prescribed torque level is achieved. Another limited slip differential mechanism is illustrated in U.S. Pat. No. 3,400,611, wherein a pair of frustro conical clutch members engage corresponding conically-shaped inner surfaces of the differential case. In that patent, springs are employed which operate through the side gears to provide a preload upon the clutch members to restrict differential action. More specifically, compression springs are placed between a pair of spaced-apart plates which have transverse walls in abutting contact with the side gears to transfer the axial load of the springs to the clutch members through the side gears. Each plate has an aperture formed in the transverse wall in alignment with a recess of an adjacent side gear so that a C-washer may be inserted during assembly of the differential to retain an axle shaft. The plate also includes inwardly directed side walls which are provided with semi-circular apertures to cooperate and surround the pinion shaft to properly locate the biasing means within the cavity between the side gears.
Since the compression springs exert a substantial axial force on the spring plates and since this force is generally spaced from the plates' zone of contact with the side gears, bending moments are created in the plates which tend to bend the plates at a thinned zone between the aperture in the transverse wall and the semi-circular apertures in the side walls. To minimize any possibility of failure at this zone, a welding bead has been provided at the intersection of the side wall and the transverse wall.